Recently, in applications such as label package serving both as a protection of a glass bottle and a PET bottle etc. and display of articles, cap sealing and accumulation package, there have been widely used stretched films (so-called heat-shrinkable films) composed of a polyvinyl chloride-based resin, a polystyrene-based resin, a polyester-based resin or the like. Of these heat-shrinkable films, a polyvinyl chloride-based film has problems that heat resistance is low, and it generates hydrogen chloride gas in incineration and causes dioxin. A polystyrene-based film has problems that it is inferior in chemical resistance, as well as an ink with a special composition needs to be used in printing, it requires high temperature incineration and generates a lot of black smoke accompanied by an abnormal odor. Therefore, as a shrink label, there has been widely used a polyester-based heat-shrinkable film which is high in heat resistance, easy to incinerate, and excellent in chemical resistance, and the use amount tends to increase being accompanied by an increase in distribution amount of PET containers.
Therefore, as a shrink label, there has been widely used a polyester-based film which is high in heat resistance, easy to incinerate, and excellent in chemical resistance, and the use amount tends to increase being accompanied by an increase in distribution amount of PET containers.
As a general heat-shrinkable polyester-based film, a film is widely utilized which greatly shrinks in the width direction. A heat-shrinkable polyester-based film in which the width direction is the main shrinkage direction as described above is stretched at a high ratio in the width direction in order to exhibit shrinkage properties in the width direction, but is often stretched at a low ratio in the longitudinal direction orthogonal to the main shrinkage direction or may not be stretched. Films stretched only at a low ratio in the longitudinal direction and films stretched only in the width direction as described above have a disadvantage that the mechanical strength in the longitudinal direction is low.
Further, a label for a bottle needs to be heat-shrunk in the circumferential direction after being attached in a ring shape on a bottle, and therefore, when a heat-shrinkable film which heat-shrinks in the width direction is attached on a bottle as a label, a ring-shaped body is formed such that the width direction of the film is set in the circumferential direction, and then the ring-shaped body needs to be cut at every prescribed length so as to be attached on a bottle. Consequently, it is difficult to attach a label made of the heat-shrinkable film which heat-shrinks in the width direction on a bottle at a high speed. Therefore, recently, a longitudinally heat-shrinkable film has been demanded which can be attached on a bottle by winding directly on the circumference of the bottle from a film roll (so-called wrap round). Further, recently, a wrapping method has been developed which keeps a one-way opening container, such as a lunch box, made of a synthetic resin in a closed state by covering the circumference of the container with a belt-like film, and a longitudinally shrinkable film is also suitable for such a wrapping application. Consequently, it is expected that a demand for a longitudinally shrinkable film will be increased in future.
Furthermore, a film made of recycled raw materials derived from PET bottles is highly demanded in terms of environmental awareness. However, since a common heat-shrinkable polyester film is obtained by using raw materials containing amorphous components in a large amount in order to provide heat shrinkage properties, the ratio of mixing recycled raw materials is limited and it has not been possible to provide a heat-shrinkable polyester-based film containing recycled raw materials in a large amount.
For example, Patent Document 1 discloses an ideal heat-shrinkable polyester film which has the main shrinkage direction in the vertical direction and has high mechanical strength in the vertical and transverse directions. However, this film contains 10 mol % or more of one or more kinds of monomer components that can be amorphous components in the whole polyester resin components, and the addition ratio of recycled raw materials is naturally limited in the upper limit.
Further, Patent Document 2 discloses, in Example 1, a heat-shrinkable film obtained by stretching an unstretched crystalline PET film at two times in the vertical direction and at 0.95 times in the transverse direction with a tube extruder. This heat-shrinkable film is a film having the main shrinkage direction in the vertical direction but is not stretched in the transverse direction and thus has low mechanical strength in the transverse direction. As described in Comparative Example 2 in Patent Document 2, the shrinkage rate in the transverse direction increases if stretching at 1.3 times is carried out in the transverse direction, and therefore, the film is not desirable as a heat-shrinkable film which is used for a label for a bottle and has the main shrinkage direction in the vertical direction. That is, according to the invention disclosed in Patent Document 2, it is difficult to obtain a heat-shrinkable film having the main shrinkage direction in the vertical direction and showing low heat shrinkage rate in the transverse direction and having high mechanical strength in the transverse direction.
Patent Document 1: JP-A-2008-179122 (claim 1 or the like)
Patent Document 2: JP-A-hei-1-127317 (Example 1 or the like)